This invention relates to an ink composition which is solid or semi-solid at room temperature, and more particularly to an ink composition including a metallic complex-type solvent dye which can be used in an ink jet recording device wherein the ink is maintained at temperatures above room temperature for extended periods of time.
Ink jet recording is superior to other recording methods because it is quiet and can print at high speed. Conventional ink compositions for ink jet recording include water based compositions. Recording is accomplished by allowing the ink to permeate into the recording paper. Unfortunately, with water based compositions, the ink drop tends to blot as it permeates fully into the paper. This is particularly true when lesser quality, absorbent paper is used. In this case, the edges of a recorded dot of ink are unclear and printing quality deteriorates.
Ink jet recording methods for eliminating defects in water based inks are disclosed in U.S. Pat. Nos. 4,390,369, 4,484,948 and 4,659,383 and Japanese Patent Application Laid-Open No. 108271/83. In these methods, a wax based hot-melt ink composition, which is solid at room temperature, is heated so that it melts and the melted ink is propelled onto the recording paper. The ink solidifies on the surface of the paper as it cools to form a recorded dot. These ink compositions have poor resistance to heat, especially when exposed to elevated temperatures over long time periods.
It is possible to improve the heat resistance of the wax based ink by addition of an antioxidant. However, solvent complex dyes, particularly metallic complex solvent dyes which have especially good heat resistance, dissolve poorly in solid waxes and can not be used. Therefore, a solvent dye having good solubility in relatively polar waxes, and having poor heat resistance is used, for example, C.I. SOLVENT BLACK 3,7. Thus, the solvent dyes used in hot-melt ink compositions tend to decompose and turn brown when subjected to high temperatures over long time periods.
Accordingly, it is desirable to develop an improved ink composition for ink jet recording which avoids these shortcomings of the prior art.